Effects of 17α-methyltestosterone on gonadal development andhormone levels in grass carp (Ctenopharyngodon idella)

By using the growth superiority demonstrated by the female individuals of the cultured grass carp, the method of breeding the whole female grass carp species by sex reversal is discussed, which has a good application prospect. The 17α-methyltestosterone (17α-MT) was selected to induce female-to-male as the male hormone, and set 4 concentration gradients evenly mixed with feed, i.e. 0 mg/kg, 50 mg/kg, 100 mg/kg, 200 mg/kg, which were respectively fed for 150 days. The objective of this study was to investigate the effects of different MT-treated diet on gonadal development and the changes of estradiol-17β (E₂), testosterone (T) and 11-ketotestosterone (11-KT), and further the characteristics in the process of grass carp sex reversal. The morphological changes of grass carp were investigated by observing the changes of gonadal structure and serum steroid hormone content at different treatment levels to explore the sex reversal. Histological sections of gonads results showed that spermatogonia began to appear in the ovaries of all treatment groups from the 30 th day after feeding. With the prolongation of feeding time, 50 mg/kg MT treatment group can inhibit the formation and maturation of oocytes, resulting in developmental delay; The inhibition of germ cells in 100 mg/kg MT treatment group was higher than that in 50 mg/kg MT treatment group, the gonads had been occupied by a large number of spermatogonia, and there was a tendency of developing testis at 210 d. The ovaries-testes state of 200 mg/kg MT treatment group at 210 d was more obvious than 50 mg/kg MT treatment group, but the number of spermatogonia was less than 100 mg/kg MT treatment group, while the control group ovary did not exhibit spermatogonia. The results of serum steroid hormone revealed that E₂ increased significantly which to some extent depended on the MT dosages, reached the highest value at 45 days and then decreased steadily, but was still significantly higher than that of the control group, however. With the development of early stage testis, E₂ level of control male also gradually increased. With the prolongation of MT feeding time, the concentrations of T in each treatment group decreased to different extents, and the biggest drop occurred in all treatment groups at 45 days, which was positively correlated with the MT concentration. The 11-KT increased to varying degrees. The results show that: 100 mg/kg was more suitable concentration to bring about sex reversal, MT can cause the early female fish serum E₂ to increase, and exert the effect of androgen, thereby promoting ovarian egg cell degradation, and spermatogonia proliferation.